What is the Difference Between HTLV 1 and 2

The main difference between HTLV 1 and 2 is that only HTLV 1 is associated with neoplasia whereas HTLV 2 is nonpathogenic.

Generally, HTLV 1 and 2 are two types of HTLVs (human T-cell lymphotropic virus), which are human retroviruses. Adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) are the two disease conditions caused by these viruses.

Key Areas Covered

1. What is HTLV 1
– Definition, Characteristics, Importance
2. What is HTLV 2
– Definition, Characteristics, Importance
3. Similarities Between HTLV 1 and 2
– Outline of Common Features
4. Difference Between HTLV 1 and 2
– Comparison of Key Differences

Key Terms

Human T-cell Lymphotropic Virus, HTLV, HTLV 1, HTLV 2

What is HTLV 1

HTLV 1 is a virus that implicates several disease conditions including adult T cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV 1 contains seven subtypes (subtypes A through G). Subtype A causes the majority of infections. Moreover, 5% of the infected people develop cancer. 

Figure 1: HTLV 1

Generally, the genome of the HTLV 1 contains two copies of single-stranded RNA that copy into the double-stranded DNA to integrate into the genome of the host. Therefore, the infection spread through dividing cells.

What is HTLV 2

HTLV 2 is a closely related virus to HTLV 1 and it has four subtypes (subtype A through D). Moreover, HTLV 2 shares 70% of genome homology with the genome of HTLV 1. Both HTLV 1 and 2 are deltaretroviruses. 

Figure 2: HTLV 1 and 2

In general, the transmission of the two HTLV viruses occurs through blood-to-blood contact in sex, through blood transfusion, and via breastfeeding. However, HTLV 2 is associated with milder neurologic disorders and chronic pulmonary infections.

Similarities Between HTLV 1 and 2

• HTLV 1 and 2 are two types of HTLV (human T-cell Lymphotropic virus), a group of human retroviruses.
• Generally, they cause a type of cancer called adult T-cell leukemia and tropical spastic paraparesis (TSP).
• Moreover, both are oncoviruses converting human lymphocytes to self-sustaining in vitro.
• In addition, they show a considerable homology in terms of genome structure, replication pattern, and properties of the structural, regulatory, and accessory proteins.
• Furthermore, the transmission of the virus occurs through infected lymphocytes by perinatal transmission and breastfeeding and through blood transfusion, sexual contact, and the use of intravenous drugs.

Difference Between HTLV 1 and 2              

Definition

Generally, HTLV 1 refers to a type of virus that infects T cells and can cause leukemia while HTLV 2 refers to a virus closely related to HTLV-I, sharing approximately 70% genomic homology (structural similarity) with HTLV-I.

Virus Entry

Moreover, the entry of the HTLV 1 occurs through GLUT-1 and NRP1 cellular receptors and heparan sulfate proteoglycans while the entry of the HTLV 2 occurs through GLUT-1 and NRP1 cellular receptors.

Clinical Impact

HTLV 1 is associated with neoplasia, adult T-cell leukemia/lymphoma (ATLL), and neurological disease termed HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP) while HTLV 2 is associated with elevated lymphocyte and platelet counts.

Geographical Distribution

Moreover, HTLV-1 is endemic in Japan, sub-Saharan Africa, South America, and the Caribbean, while HTLV-2 is prevalent among the indigenous populations in Africa and the Indian-American tribes in Central and South America as well as among drug users in Europe and North America.

Preferred Cell Types

HTLV 1 prefers CD4+ T lymphocytes while HTLV 2 prefers CD8+ T lymphocytes.

Conclusion

In brief, HTLV 1 and HTLV 2 are two types of HTLV (human T-cell Lymphotropic virus). Both are retroviruses. Generally, HTLV 1 causes neoplasia but HTLV 2 does not cause neoplasia. The two main diseases associated with the HTLV 1 is T cell lymphoma and tropical spastic paraparesis. However, HTLV 2 is non-pathogenic and can cause elevated lymphocyte and platelet counts. Therefore, the main difference between HTLV 1 and 2 is their pathology.   

References:

1. Ciminale V, Rende F, Bertazzoni U, Romanelli MG. HTLV-1 and HTLV-2: highly similar viruses with distinct oncogenic properties. Front Microbiol. 2014 Jul 29;5:398. doi: 10.3389/fmicb.2014.00398. PMID: 25120538; PMCID: PMC4114287.
2. “Human T-Lymphotropic Virus.” Wikipedia, Wikimedia Foundation, 10 Jan. 2022.

Image Courtesy:

1. “HTLV-1 and HIV-1 EM 8241 lores” By CDC – Own work (Public Domain) via Commons Wikimedia
2. “HTLV Phylogeny” By Tylercj2 – Own Work (CC BY-SA 4.0) via Commons Wikimedia